Variable displacement pump



C. A. L. RUHL VARIABLE DISPLACEMENT PUMP April 23, 1963 2 Sheets-$heet 1Filed May 9, 1960 INVENTOR CharlesALRuhl BY 2%Mw ATTORNEYS April 23,1963 c. A. L. RUHL 3,086,477 VARIABLE DISPLACEMENT PUMP 2 Sheets-Sheet 2Filed May 9, 1960 FieB IN VENTOR CharlesALBuhl BY M ATTORNEYS UnitedStates Pater 3,086,477 VARIABLE DI PLACEMENT PUMP Charles A. L. Ruh],Kalamazoo, Mieh., assignor to The New York Air Brake Company, acorporation of New Jersey Filed May 9, 1960, Ser. No. 27,707 1 Claim.(Cl. 103-161) This invention relates to fluid pressure engines of thereciprocating piston type wherein the pistons are mounted in radialcylinder bores. The term engine is used herein in its generic sense andit will be understood that it includes motors as well as pumps.

The object ofthis invention is to provide an improved mechanism forvarying the displacement of this kind of eng1ne.

According to the invention, there is provided a cylindrical cam memberwhich has an inner peripheral surface that is coaxial with the cylinderbarrel and which is in operative engagement with the pistons at theirouter ends for moving them on their discharge strokes during relativerotation between the cylinder barrel and the cam member. This innerperipheral surface is a smooth compound curve which connects atransverse circular contour at one axial location with a transversegenerally elliptical contour at a spaced axial location; the minordiameter of the generally elliptical contour and the diameter of thecircular contour being equal. Relative longitudinal movement between thecylinder barrel and the cam member along their common axis causes thepistons to engage generally elliptical contours of varying majordiameters and thus results in a gradual change in the length of thestrokes of the pistons; the length of the strokes decreasing as thepistons draw nearer the circular contour.

The preferred embodiment of the invention will now be described indetail with reference to the accompanying drawings, in which:

FIG. 1 is an axial sectional view of a rotary cylinder barrel pumpincorporating the invention; the arcuate inlet and discharge ports beingrotated into the plane of section for a clearer understanding of thearrangement of the parts.

FIG. 2 is a sectional view taken on line 22 of FIG. 1.

FIG. 3 is a view of the inner face of housing section 11 showing thearrangement of the arcuate inlet ports, a portion of the section havingbeen broken away to show one of the passages connecting the inletmanifold with the arcuate ports.

FIG. 4 is a sectional view taken on line 44 of FIG. 1.

FIG. 5 is an enlarged sectional view taken on line 5--5 of FIG. 4showing one of the O-ring encircled biasing areas on the rear face ofthe valve plate.

As shown in the drawings, the pump comprises a housing having twoseparable sections 11 and 12 which are connected by bolts (not shown).Extending into the housing is a drive shaft 13 which is journalled inhousing section 11 and in a ball bearing 14 carried by the housingsection 12, and which is connected in driving relation with a rotarycylinder barrel 15 by splines 16. The rotary cylfinder barrel 15 isprovided with four pairs of diametrically opposed cylinder bores 17,each of which receives a reciprocable piston 18 whose outer end carriesa spherical surface 19 which is centered on the longitudinal axis of thepiston.

A plurality of bores 21 extend through the cylinder barrel 15 and arearranged so that one intersects the inner end of each cylinder bore 17.The right ends of these bores, as viewed in FIG. 1, are positioned toregister successively with four equi-angularly spaced arcuate ports 22,23, 24 and 25 formed in the inner end face of housing section 11. Theseports are spaced apart a distance equal to the diameter of bore 21. Twoof these ports, namely 22 and 24, communicate with the inlet port 26formed in housing section 12 through radial passages 27 and 28,respectively, and the annular inlet manifold 29, and the other two ports23 and 25 are blind and function merely as balancing chambers. The leftends of the through bores 21 are positioned to register with foursimilar arcuate ports 22', 23', 24 and 25 iormed in the front face ofvalve plate 3-1 which floats freely between housing section 12 andcylinder bar-rel 15 but which is prevented from rotating by a pin 32.The arouaate ports 23 and 25, which are directly opposite ports 23 and25, communicate with bores 33 and 34, respectively, that extend throughthe valve plate 31 and connect with the longitudinal legs 35 (only oneshown in FIG. 1) of a discharge manifold 36. This manifold 36 leads intodischarge port 37 formed in housing section 12. The rear face of thevalve plate 31 is provided with two counterbores 38 (one being shown inFIG. 5) which are coaxial with the bores 33 and 34 and which receive theresilient O-rings 39 which are squeezed between the valve plate 31 andhousing section 12. The regions enclosed by the outer margins of theseO-rings define biasing areas which are subject to discharge pressure andwhich develop forces that urge the valve plate 31 into sealingengagement with the cylinder barrel and, in turn, urge the cylinderbarrel into sealing engagement with the inner end face of housingsection 11. The arcuate ports 22' and 24', which are directly oppositeports 22 and 24, are blind and, as in the case of ar-cuate ports 23 and25, serve merely as balancing chambers.

Housing section 12 is provided with a stepped bore 41 which receives asliding cylindrical cam member 42. The cam member 42 is prevented fromrotating by an integral key 40 which slides in a longitudinal slotformed in housing section 12. A portion 43 of the inner peripheralsurface of cam member 42 takes the form of :a smooth compound curvewhich connects a transverse circular contour 44 at one axial positionwith a transverse generally elliptical contour 45 at an axially spacedposition; the elements of the surface portion 43 being straight lines.The generally elliptical contour comprises two circular arcs centered atthe points 46 and 47 (see FIG. 2) and two straight portions which aretangent to and connect the adjacent ends of the two arcs. The minordiameter of the generally elliptical contour is the same as the diameterof the circular contour 44. The surface portion 43 engages the sphericalouter ends 19 of the pistons 18 and serves, during rotation of thecylinder barrel, to move the pistons on their discharge strokes. Sincetransverse planes intersecting surface portion 43 at different axialpositions between contours 44 and 45 cut generally elliptical contoursof varying major diameters, the longitudinal position of cam member 42relative to cylinder barrel 15 determines the lengths of the pistonstrokes.

The position of cam member 42 can be regulated in several differentways, but in the preferred embodiment it is controlled automatically bya discharge pressure compensator. In this embodiment, the cam member 42is biased toward its maximum displacement-establishing position (shownin FIG. 1), wherein its left end is in abutment with housing section 12,by a coil compression spring 48 and is moved in the opposite directionagainst this bias by a fluid pressure control motor 49 which includes anannular Working chamber 51 and an annular piston 52. The pressure in theworking chamber 51 is controlled by a valve 53 which is connected withit by a passage 54. The control valve 53 comprises a bore 55 formed inhousing section 12 and interconnecting inlet and exhaust ports 26 and37, and a plunger 56 carrying a tapered nose 57 that defines a controledge 58 and an enlarged portion 59 that acts as a stop to limit leftwardmovement. The bore 55 is encircled by an annular chamber 61 whichcommunicates with passage 54. Plunger 56 is formed with twodiametrically opposed flats which, together with aligned longitudinalslots 62 in enlarged portion 59 and the bore 55, define flow passages 63and 64 that are in continuous communication with inlet port 26 throughthe right end of bore 55. The valve plunger 56 is biased to the positionshown in FIG. 1 by a coil compression spring 65 and, in this position,the left ends of the flats extend into chamber 61. The plunger 56 isshifted in the opposite direction by the discharge pressure in port 37which acts upon the nose 57.

Operation When the pump is put in operation, the drive shaft is rotatedin the direction of the arrow in FIG. 2 and the parts are in thepositions shown in FIG. 1. All of the pistons are urged outward in theradial direction into contact with the cam member 42 by centrifugalforce and that pair of pistons 18 in the regions A of the ellipticalcontour will move outward relatively to their cylinder bores. Thethrough bores 21 associated with these pistons will, at this time, be incommunication with the arcuate ports 22 and 24 so that fluid enteringinlet port 26 may flow to their cylinder bores through manifold 29,radial passages 27 and 28, and the arcuate ports 22 and 24. Those bores21 associated with the pair of pistons in the regions B of theelliptical contour register with arcuate ports 23 and 25, and the inwardmovement imparted to these pistons by the cam member 42 will cause themto discharge fluid through arcuate ports 23 and 25', bores 33 and 34,legs 35, manifold 36, and discharge port 37. The remaining two pairs ofpistons 18 are at their outermost or innermost positions and thus theywill neither draw in or expel fluid. An inspection of FIG. 2 will showthat each piston 18 completes two pumping cycles, each comprising aninlet and discharge stroke, during each revolution of the cylinderbarrel 15. It also will be apparent that the use of pairs ofdiametrically opposed pistons results in a balance of the radialcomponents of the thrust forces transmitted between pistons 18 and cammember 42.

As long as the discharge pressure in port 37 is below that valuerequired to produce a force on nose 57 which is greater than the bias ofspring 65, valve plunger 56 will remain in the FIG. 1 position and theworking chamber 51 of control motor 49 will be vented through passages63 and 64 and through the restricted passage 66 formed in the cam member42. Because of this, spring 48 will keep the cam member 42 in the FIG. 1position and the length of the piston strokes will be a maximum.

When the demand for high pressure fluid decreases to such an extent thatthe discharge pressure force acting on nose 57 becomes greater than theforce of spring 65, valve plunger 56 shifts to the right and closes thevent passages 63 and 64. Simultaneously control edge 58 overtravelsannular chamber 61 and opens a path from discharge port 37 to workingchamber 51 through passage 54. Due to the fact that nose 57 is tapered,rightward movement of plunger 56 permits a progressively greaterquantity of fluid to flow to working chamber 51 and, since the fluid inthe working chamber can escape only through the restricted passage 66,this results in a rising pressure in the working chamber. When the forcedeveloped on annular piston 52 by the pressure in working chamber 51becomes greater than the bias of spring 48, cam member 42 moves to theright. This shift of the cam member 42 has the effect of presenting tothe pistons 18 a generally elliptical cam surface of smaller majordiameter and this results in a decrease in the lengths of the pistonstrokes and in the displacement of the pump. As discharge pressurecontinues to rise, the pressure in working chamber 51 increases and cammember 42 moves further to the right. When discharge pressure reachesthe 4 desired maximum, cam member 42 will be in a position in whichcircular contour 44 is in engagement with the pistons. At this time,rotation of cylinder barrel 15 is ineffective to reciprocate the pistons18 and the displacement of the pump is zero.

When the demand for high pressure fluid increases, discharge pressuredecreases and valve plunger 56 moves to the left thereby reducing theflow to and consequently the pressure in working chamber 51. Spring 43now shifts cam member 42 to the left and thus causes it to increaseprogressively the lengths of the piston strokes. When the valve plunger56 again vents working chamber 51, cam member 42 returns to the FIG. 1position.

During operation of the pump, the point of contact between the surface43 and the spherical end 19 of each piston 18 is always displaced to theleft, as viewed in FIG. 1, from the longitudinal axis of the piston.This arrangement has two desirable effects. First, it producesunidirectional rotation of the pistons 18 in their cylinder bores andthus minimizes wear on ends 19. Second, it causes the axial componentsof the thnust forces transmitted between the pistons 18 and the cammember 42 to act to the right in FIG. 1 and urge cylinder barrel 15 intosealing engagement with the inner end face of housing section 11.

As stated previously, the drawings and description relate only to apreferred embodiment of the invention. Since many changes can be made inthe structure of this embodiment without departing from the inventiveconcept, the following claim should provide the sole measure of thescope of the invention.

What is claimed is:

A fluid pressure engine comprising a housing containing high and lowpressure ports; a drive shaft journaled in the housing; a rotarycylinder barrel connected in driving relation with the shaft but beingfree to move longitudinally of it, the cylinder barrel containing aplurality of pairs of diametrically opposed radial cylinder bores;longitudinal flow passages formed in the cylinder barrel, one passageintersecting each cylinder bore and each passage opening through theside faces of the cylinder barrel; a reciprocable piston in eachcylinder bore, each piston having a spherical outer end; a steppedcylindrical bore formed in the housing coaxial with and encircling thecylinder barrel, the bore having a step which divides it into a smalldiameter portion and a large diameter portion; a cylindrical cam ringguided for sliding movement in the cylindrical bore and formed with ashoulder on its outer periphery that defines small and large diameterportions which fit the small and large diameter portions, respectively,of the cylindrical bore, the cam ring having an inner peripheral surfacewhich engages the outer ends of the pistons and which is a smoothcompound curve that connects a transverse circular contour at one axialpositon with a transverse generally elliptical contour at a spaced axialposition, the diameter of the circular contour being equal to the minordiameter of the generally elliptical contour; means for transmittingfluid under pressure to the shoulder on the cam ring to thereby developa pressure force that shifts the cam ring longitudinally in thecylindrical bore; a coil compression spring coaxial with the cylinderbarrel and reacting between the housing and the cam ring for opposingmovement of the cam ring under the action of said pressure force; meansfor preventing rotation of the cam ring relatively to the housing; astationary valve face carried by the housing and lying in a plane thatis normal to the axis of rotation, the valve face containing a pair ofdiametrically opposed low pressure ports and a pair of diametricallyopposed balance ports arranged to register sequentially with thelongitudinal flow passages as the cylinder barrel rotates, the valveface being so located that the cylinder barrel is urged toward it by theaxial components of the reaction forces developed between the pistonsand the cam ring; a nonrotary floating valve plate, having a valvingface located in a plane that is normal to the axis of rotation,positioned at the side of the cylinder barrel opposite the stationaryvalve face, the valve plate contining a diametrically opposed pair ofhigh pressure ports aligned with the balance ports in the stationaryvalve face and a diametrically opposed pair of balance ports alignedwith the low pressure ports in the stationary valve face, the ports inthe floating valve plate being arranged to register sequentially withthe longitudinal flow passages as the cylinder barrel rotates; meansresponsive to the pressure in the high pressure ports for urging thevalve plate toward the cylinder barrel; and flow passages connecting thehousing high and low pressure ports with the corresponding ports in thestationary valve face and in the valve plate.

References Cited in the file of this patent UNITED STATES PATENTS2,698,585 Cotner et a1. Jan. 4, 1955 2,703,054 Heater Mar. 1, 19552,809,594 Orshansky Oct. 15, 1957 2,872,875 Mergen et al Feb. 10, 195910 2,895,426 Orshansky July 21, 1959 FOREIGN PATENTS 434,962 GermanyOct. 6, 1926

